A study will be made of the physical, and biochemical mechanisms of interaction between proteolytic enzymes and naturally occurring protein inhibitors in proteolytic enzymes. Inhibitors and enzymes of differing physical and chemical properties and different specificities will be used. The enzymes will include: trypsin, alpha-chymotrypsin, subtilisin, and elastase. The inhibitors will include: avian ovomucoids, avian ovoinhibitors, lima bean inhibitor, Kunitz pancreatic inhibitor, chicken serum inhibitors, and human serum alpha-trypsin inhibitor. The interactions will be characterized by physical and chemical methods including ultracentrifugation, gel electrophoresis and filtration, spin and nuclear magnetic labelling, and other similar methods. Chemical modification of the structures of the enzymes and the inhibitors will be a primary tool. BIBLIOGRAPHIC REFERENCES: Feeney, R. E. and Osuga, D. T., "Purification of chemically modified proteins" pp. 127-160 IN: Methods of Protein Separation 1, N. Catsimpoolas, Editor, Plenum Press, New York (1975). Feeney, R. E., Blankenhorn, G., and Dixon, H. B. F., "Carbonyl-amine reactions in protein chemistry" Advances in Protein Chemistry 29, 135-203 (1975).